Return Value

For an
triangleMode-triangular matrix (IsUpperTriangular
is ), you try to set an component
below the diagonal.

-or-

For a lower-triangular matrix
(IsLowerTriangularis ), you
try to set an component above the diagonal.

-or-

The matrix has IsUnitDiagonal set
to , and you try to set a diagonal component.

Remarks

This method does not perform bounds checking. It is provided
for optimized access in situations where the arguments are known to be
within bounds. If either argument is outside its valid range, the effect
may be unpredictable.